A pulse-type radar system emits a sequence of pulses as transmission waves after being modulated to have a predetermined frequency and receives reflected waves which are reflections of the transmission waves from an object. The system then determines distance to the object by measuring the time it takes for the reflected waves to return. The pulse-type radar system uses high frequency signals in which different frequencies are used respectively for transmission and reception to determine a differential frequency as an intermediate frequency signal. The distance to the object is measured by means of calculating the time it takes for the intermediate frequency signal to have its maximum amplitude. See Takashi YOSHIDA, “Radar Engineering Revised Edition”, The Institute of Electronics, Information and Communication Engineers, Oct. 1, 1996, p. 74-75 and p. 175-177 (YOSHIDA).
Some pulse-type radar systems utilize heterodyne detection in which a high frequency oscillator is used for both the transmission unit and the reception unit. Heterodyne radars require a lot of millimeter-wave components such as a circulator or a directional coupler, to deal with millimeter-wave signals. Heterodyne radars use two high frequency oscillators and use a lot of millimeter-wave heterodyne radars, which limits miniaturization and cost reduction of the radar.
Thus, some radars use a homodyne detector in which a signal from a single high frequency oscillator is modulated in a transmission unit and is also used for a frequency conversion in a reception unit. Homodyne radar systems share a signal from a single high frequency oscillator for both the transmission unit and the reception unit, so that they can be reduced in size and costs in comparison with heterodyne radar systems. Japanese Patent Laid-open No. 2006-177983 shows a homodyne pulse radar system.
Pulse radar according to Japanese Patent Laid-open No. 2006-177983 emits a high frequency signal converted by means of ASK (amplitude shift keying) technique with a high speed square wave signal. The converted output is then reflected from an object as reflected wave. The reflected wave is used as a reception signal. Then logical AND operation is performed on the reception signal and a gating signal which is a delayed result of the high speed square wave signal. A delay time of the gating signal at which the maximum output level is obtained represents a delayed time of the reception signal. The distance to the object is calculated according to this delay time
Conventional homodyne radar systems can be practically reduced in size and cost than heterodyne radar systems. However, even in the radar system according to Japanese Patent Laid-open No. 2006-177983, there are two line units for both the transmission and reception. A number of parts are still required. This can complicate the structure or reduce the yield of good products.
An object of the present invention is to provide a smaller radar system with the reduced number of component parts as much as possible which can easily be structured at lower cost than in conventional systems. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.